This invention relates generally to gas turbine engines, and more particularly to turbine flowpath components made of a low-ductility material in the turbine sections of such engines.
A typical gas turbine engine includes one or more turbine rotors which extract energy from the primary gas flow. Each rotor comprises an annular array of blades or buckets carried by a rotating disk. The flowpath through the rotor is defined in part by a shroud, which is a stationary structure which circumscribes the tips of the blades or buckets. These components operate in an extremely high temperature environment, and must be cooled by air flow to ensure adequate service life. Typically, the air used for cooling is extracted (bled) from the compressor. Bleed air usage negatively impacts specific fuel consumption (“SFC”) and should generally be minimized.
It has been proposed to replace metallic shroud structures with materials having better high-temperature capabilities, such as ceramic matrix composites (CMCs). These materials have unique mechanical properties that must be considered during design and application of an article such as a shroud segment. When compared with metallic materials, CMC materials have relatively low tensile ductility or low strain to failure, and a low coefficient of thermal expansion (“CTE”).
CMC materials expand at different rates than surrounding metallic hardware, and are not as suitable as metals for forming small-scale mounting features such as hooks, grooves, rails, and the like. Conventional mechanical clamped joints are sometimes dependent on frictional forces which can be inconsistent when using a combination of metallic and CMC materials.
Accordingly, there is a need for a turbine flowpath structure which is light weight and high-temperature resistant, with a predictable mounting configuration.